1. Field of the Invention
The present invention relates to a laser system for surgery, particularly ophthalmic surgery, employing fiber optics for directing laser energy to the body. More particularly, the invention relates to the use of a laser in the mid-infrared wavelengths for providing low laser energy through a compound optical fiber arrangement for ophthalmic and other surgical purposes.
2. Background Prior Art
Devices have long been sought for the removal of intraocular pathological tissue and for fragmentation and liquefaction of eye lenses by the use of relatively low energies, particularly for removal of cataracts. One known device, a Kelman Phakomulsifier, has been used by eye surgeons in the removal of cataracts from the eye and an ocutone has been used to cut vitreous strands and membranes.
The Kelman Phakomulsifier which functions by the mechanical lysis of the lens has certain limitations in its use relating to (1) the amplitude of the shockwave introduced in the eye, (2) the amount of aspiration required to remove a fragmented lens, (3) the amount of energy placed in the eye and (4) the general dispersion of the energy in the eye.
The ocutone and other available vitrectomy devices also rely on mechanical action. Sectioning of vitreous strands and removal of membranes is accomplished using miniature oscillating or rotating surgical blades. Accurate positioning of these instruments with respect to these often diaphanous bands is particularly difficult, as is operation on membranes adjacent to the retina.
Applicants have discovered that laser energy, even low energies, at wavelengths above 1.8 microns and, in particular, the energy at the wavelength of a holmium (Ho:YAG) laser, approximately 2 microns and the energy at the wavelength of an Er:YAG laser, approximately 3 microns, are especially useful in ophthalmic surgery.
The present invention is based in part on this discovery and in part on the development of an adequate optical system for delivery of these energies to the operative site.
Providing a delivery system for 3 micron laser energy immediately encounters certain obstacles. A fiber optic delivery approach would be preferred for simplicity and directivity of the energy and fluorozirconate or fluoride glass fiber would be the optic element of choice. Fluoride glass fiber is, however, relatively fragile, toxic to tissue and reactive in water. While the fluoride glass fiber may be jacketed for support and hermetically-sealed to prevent contact with water, the resultant fiber may be too thick and cumbersome for delicate eye surgery.
Quartz fiber, while known to be non-toxic, rugged and useful for visible and near infrared applications, is generally considered as being unusable for transmission of light beyond 2.4 microns because of its large attenuation of laser energy at these wavelengths.
It is known from the prior art (U.S. Pat. No. 4,273,109) to employ two interconnected fibers having different diameters for the transmission of laser energy in surgical situations. It is also known to employ a protective sheath around optical fiber for hermetic sealing purposes (U.S. Pat. No. 4,669,818).